Electrical connections using discrete, electrically-conductive particles

ABSTRACT

An electric heater for a rear windscreen of a motor vehicle including a heater element constituted by a thin strip of electrically resistive material and a pair of terminals clamped to respective ends of the element, has discrete electricallyconductive particles disposed between the ends of the element and the terminals to establish electrical connection therebetween. The strip is coated on one surface with a layer of adhesive to facilitate mounting of the element on the windscreen, and the particles adhere to the adhesive layer at the ends of the strip and impinge on the element through the adhesive layer.

United States Patent i191 111 83,242 Barnard Jan. 1, 1974 [54]ELECTRICAL CONNECTIONS USING 2,982,934 5/1961 Browne 338/309 X DISCRETE,ELECTRICALLY-CONDUCTIVE 6&5 PARTICLES 3,529,074 9/1970 Lewis; [75]Inventor: Dominic Paul Edmund Barnard, 3,535,494 10/1970 Armbruster219/543 X Witney, England Primary Examiner-Darrell L. Clay [73]Assignee. grrrliggnlgdustnes Limited, London, Att0mey wmiam D. Ha Vet a1[22] Filed: Apr. 25, 1972 [57-] I ABSTRACT [21] R 5 ,7 w An electricheater for a rear windscreen of a motor 30 Foreign Application PriorityData vehicle including a heater element constituted by a thin strip ofelectrically resistive material and a pair of A 1971 Great mam396/Uterminals clamped to respective ends of the element, [52] us Cl 219/546,29/621 29/628, has discrete electrically-conductive particles disposed174/84 C 338/309 339/276 T between the ends of the element and theterminals to [51 Im. Cl. 1105b 3/02 establish electrical connectiontherebetween- The Strip [58] Field of 7 4 88 R, 1 17 is coated on onesurface with a layer of adhesive to fa- 2 9/541 54 543 549 522 338/30932 cilitate mounting Of the element on the windscreen, 332; 29/628 610619 621, 629; 339/276 R and the particles adhere to the adhesive layerat the 276 T ends of the strip and impinge on the element through v theadhesive layer. [56] References Cited 11 Claims, 4 Drawing FiguresUNITED STATES PATENTS I 2,961,522 11/1960 Hammer 2l9/543 X ZZZ////////SHEET 10F 2 PATENTEDJAH 1 I974 ELECTRICAL CONNECTIONS USING DISCRETE,ELECTRICALLY-CONDUCTIVE PARTICLES This invention relates to electricalconnections and, more particularly, to methods of establishingelectrical connections, and also to devices that include electricalconnections.

A problem has been experienced in establishing a reliable electricalconnection to a very thin conducting element, for example, to flexiblemetallic foil. It has been proposed that this problem may be overcome byclamping the element between two substantially rigid metal plates and byproviding at least one of the metal plates with a plurality of sharpprojections which bite into the surface of the conducting element. Theconnection so established is not entirely satisfactory in practicebecause the projections tend to tear the conducting element. Furthermoresuch a connection suffers from the disadvantage that expense is involvedin the necessary preforming of the metal plate to provide the sharpprojections.

It is an object of the present invention to provide a solution to theproblem which is satisfactory in practice and which obviates the needfor the preforming operation.

According to a first aspect of the present invention there is provided amethod of establishing an electrical connection between a pair ofelectrically-conductive members by clamping the members to one another,

- characterised by the provision of discrete, electricallyconductiveparticles between the members.

Preferably the method includes the steps of coating one of the memberswith a layer of adhesive, and'of causing the particles to adhere to theadhesive layer.

According to a second aspect of the present invention there is provideda device that includes an electrical connection, comprising first andsecond electrically-conductive members, and discrete,electricallyconductive particles under pressure between the members toestablish electrical connection therebetween.

Preferably the first member is coated with a layer of adhesive, and theparticles adhere to this layer and impinge on the first member throughthe adhesive layer.

The adhesive may be a thermo-setting adhesive.

The particles may be of metal.

The first member may be a relaitvely thin conducting element.

The element may be clamped between the second member and a thirdelectrically-conductive member, and, in such a case, a pad of resilientmaterial may be interposed between the element and the third member.

According to a third aspect of the P esent invention there is providedan electric heater comprising a heater element in the form of a strip ofelectrically resistive material, a pair of terminals for establishingelectrical connection to respective ends of the element, and discrete,electrically-conductive particles disposed under pressure between theelement and each terminal.

Preferably the element is coated on one surface with a layer of adhesiveto facilitate mounting of the element on a surface to be heated, and theparticles adhere to the adhesive layer and impinge on the elementthrough the adhesive layer.

The surface of the element remote from the adhesive layer may havebonded thereto a layer of electrically insulating material.

The element may be supported by a readily removable backing layer.

One form of electric heater, for a glass rear windscreen or a window ofa vehicle, including an electrical connection in accordance with thepresent invention will now be described, byway of example, withreference to the accompanying drawings in which:

FIG. 1 is a partly-broken-away plan view of the heater;

FIG. 2 is an enlarged perspective view of part of a terminal for theheater;

FIG. 3 is an enlarged, exploded view of the terminal on the line III-IIIof FIG. 1 prior to final assembly of the terminal; and

FIG. 4 is an enlarged end view of the terminal after final assembly.

The heater of FIG. 1 is manufactured as follows. A rectangular laminatedsheet, approximately 23% in (60 cm) long by 10 in (25 cm) wide andapproximately 0.0015 in (38 pm) thick, is produced comprising a layer ofaluminium foil bonded to a layer of plastics material film, for example,a polyester such as that sold in the United Kingdom under the Trade MarkMELINEX. Preferably the metal foil layer and the plastics film layerhave similar thicknesses. The exposed surface of the aluminium foillayer (that is, that surface opposite the plastics film layer) is coatedwith a cross-linked, acrylic-based thermosetting adhesive coating, and afairly thick sheet of backing paper or card having similar rectangulardimensions is then applied to this adhesive-coated surface. The backingis conveniently a polythene coated, silicone release, heavy Kraft paperwhich has a polished or smooth surface to render it readily separablefrom the aluminium foil and polyester film laminated sheet.

The so formed sheet is subjected to a stamping operation from thepolyester film side (that is, the side opposite the backing paper). Thepattern that is stamped is one of long narrow strip form such that thestrip follows a sinuous path. As shown in FIG. 1, this sinuous pathcomprises four generally parallel sections of substantially similarlongitudinal extent, the sections having respective pairs of parallelcoextensive lengths 2 and 3, 6 and 7, 8 and 9, and 11 and l2 extendinglongitudinally of the said so-formed sheet. The lengths 2 and 3 of thefirst section are joined to one another at one end by a short end piece4 and at the opposite end by an end piece 5 that continues on and formsthe end piece at one end of the lengths 6 and 7 of the second section.The opposite ends of the lengths 6 and 7 are joined to one another andto one end of the lengths 8 and 9 of the third section by an end piece10. Similarly, the opposite ends of lengths 8 and 9 are joined to oneanother and to one end of the lengths 11 and 12 of the fourth section byan end piece 13. The opposite ends of lengths l1 and 12 are joined toone another by an end piece 14 that continues on towards the firstsection where it terminates in a wider portion 15. An adjacent .issufficient to pass wholly through both the aluminium foil and thepolyester film and slightly into, but not through, the backing paper..-

Thus as shown in FIG. 1, the sheet of backing paper 20 supportsadhesively only a long, narrow sinuous strip 22 (of aluminium foil 24bonded to polyester film 26) after the remaining larger area residue(not shown) of the aluminium foil 24 and the polyester film 26 has beenpeeled away from the sheet of backing paper 20.

Another paper sheet 25 (only part of which is shown), having similar.dimensions to sheet 20, is coated on one side surface with a low-tackadhesive. This adhesive-coated surface is applied to the sheet 20supporting the strip 22 so that the strip 22 is sandwiched between thesheets 20 and 25. The thickness of the sheet 25 is not very importantalthough the thicker it is the more rigid support it will give to thestrip 22 during installation (described below). The sheets 20 and 25 areformed with an M-shaped cut-out adjacent one corner in the vicinity ofthe end portions 15, 16 of the strip 22. These end portions and 16 areelectrically connected to respective terminals 30 in the followingmanner.

The backing sheet is partially peeled away from said one corner toexpose the strips end portions 15 and 16. Each of the adhesive-coatedexposed portions 15 and 16 is impregnated with steel filings 27 whichare sharp or have an irregular surface and which adhere to the adhesivecoating (referenced 28 in FIGS. 3 and 4). The portion is then placed,filings downwards, within a respective short channel-sectioned brassmember 31 (FIG. 2) so that the steel filings are in contact with a base32 of the member 31 (see FIG. 3). The base 32 is slightly curvedconvexly to the interior of the channel, and is formed integrally withthe terminal 30. A pad 33 of sulphur-free chloroprene rubber is placedupon the sheet above the base 32 and covered by a slightly bowed metalplate 34. The side walls of the member 31 are then bent over to clampthe two side margins of plate 34 and sandwich between the plate 34 andbase 32, the pad 33, the sheet 25, the end portion 15 (and 16), and thesteel filings adhesively attached thereto. The clamping pressure is suchas to straighten both the base 32 and the plate 34 and press the steelfilings 27 through the adhesive coating 28 into the aluminium foil 24 soas thereby to make a low resistance, electrical connection between thealuminium foil 24 of the strip 22 and the base 32 of the brass member 31through the adhesive coating 28. The terminals are in the form of bladeconnectors.

The steel filings 27 are of a particular size such that in a sieveanalysis carried out as detailed in British Standards Specification1796:1952, all of the filings 27 pass through a No. 60 British Standardmesh (that is, a mesh having 60 apertures per inch) but not through aNo. 200 British Standard mesh, and at least 45 percent of the. filings27 pass through a No. 100 British Standard mesh but not through a No.150 British Standard Mesh. Nos. 60, 100, 150 and 200 British Standardmeshes, according to British Standards Specification 410:1969, havenominal aperture sizes of 250 m, 150 pm, 160 pm, and 75 pm respectively(that is to say when formed of wire cloth the preferred average wirediameter is approximately 160 am, 100 um, 71 um, and 50 pmrespectively). The steel filings or chips are conveniently of a rustlessor stainless steel, such as a steel within the En 56 range of BritishStandards Specification 970:1955, and that prior to filing has a Brinell4 Hardness No. in the range 201 to 255. Preferably the steel is thatknown as 8.8. 9702En 56 AM/R which has between 12.0% and 14.0% chromiumand no more than 0.12% carbon, 1.00% silicon, 1.50% manganese, 1.00%nickel, 0.75% sulphur, 0.045% phosphorus, 0.60% molybdenum, 0.60%selenium, 0.60% zirconium and 0.35% lead (the total of the last fourconstituents being no more than 1.00%).

Each terminal 30 is completed (see FIG. 4) by snapping a semi-rigidpolyvinylchloride cover 35 on to the bent-over side walls of member 31to cover them and the exposed portion of plate 34, and by adhesivelyattaching to the underside of the base 32 a pad 36 having its lowerexposed surface treated with a contactadhesive.

The strip 22 is installed in a vehicle in the following manner so thatthe element constituted by its aluminum foil part 24 can be used as arear glass windscreen (or window) heater. The interior glass surface isfirst cleaned with methylated spirit and allowed to dry. The backingsheet 20 is then peeled away from the strip 22 which is thus leftadhesively mounted on the sheet 25. The strip 22 supported by sheet 25is placed to the screen so that the low tack adhesive of the sheet 25and the thermosetting adhesive 28 covering the aluminium foil part 24 ofstrip 22 contact the clean interior surface of the glass. The strip 22and the terminals 30 are pressed firmly to the glass and adhere theretoby the adhesive on the strip 22 and on the pads 36. A check for goodadhesion is obtained by viewing the exterior surface of the glass (thatis, from the outside of the vehicle) to see that there are no airbubbles. The supporting sheet 25 is then stripped off starting at thecorner furthest from the terminals 30, and torn off at the terminalswhose edges may be used as cutters. A short electrical lead or wirehaving a female tag connector at one end connects one blade connectorterminal 30 to an earth point on the vehicle body; and another, long,electrical lead or wire similarly connects the other blade connector 30via a dashboard-mounted electric ON/OFF switch to a battery voltagepoint that is only energised when the vehicle ignition is ON. If desireda warning light can be fitted by wiring it between the side of theswitch towards the aluminium heater element 24 and earth. Such a warninglight can be incorporated in the apparatus sold by Smiths IndustriesLimited under the Trade Mark WARNALITE. Furthermore, the electric ON/OFFswitch may be such as that described in US. Pat. No. 3,731,021.

When the installed heater is first used, the heat cures thethermosetting adhesive 28 to provide for pennanent installation of theheater, and the heater is then usable for demisting and defrostingpurposes.

I claim:

1. An electric heater comprising a heating element which is ofelectrically resistive material in strip form and which has two ends anda pair of opposed surfaces, a coating of adhesive on one surface only ofthe said element to facilitate mounting of the said element'on a surfaceto be heated, a pair of terminals electrically connected to respectivesaid ends of the element, each terminal comprising anelectrically-conductive member, means clamping each said member to thesaid element, and discrete, electrically-conductive particles adheringto the said adhesive coating at the said ends of the element anddisposed under pressure between each of said members and the saidelement impinging onto the said element through the said adhesivecoating establishing electrical connection between the said members andthe respective said ends of the element.

2. An electric heater according to claim 1, wherein the said adhesive isa thermo-set adhesive.

3. An electric heater according to claim 1, wherein the surface of thesaid element remote from the said adhesive coating has bonded thereto alayer of electrically insulating material.

4. An electric heater according to claim 1, wherein the ends of the saidelement are of enlarged width.

5. An electric heater according to claim 1, wherein the said elementfollows a sinous path.

6. An electric heater according to claim 1, wherein the said element issupported by a readily removable backing layer.

7. An electric heateraccording to claim 1, wherein the said adhesivecoating extends over the whole of the said one surface of the element.

8. A method of establishing an electrical connection between'anelectrically-conductive member and a thin electrically-conductiveelement which is to be supplied with electric current and which has apair of opposed surfaces, comprising the steps of a. applying a coatingof adhesive to one surface only of the said element,

b. applying discrete, electrically-conductive particles to a part of thesaid adhesive coating,

0. bringing the said member into contact with the said particles, and

d. clamping the said member and the said element together causing thesaid particles to impinge onto the said element through the saidadhesive coating providing the said electrical connection between thesaid member and the said element.

9. A device that includes an electrical connection comprising a thinelectrically-conductive element having first and second opposedsurfaces, an electricallyclamping means includes a plurality of deformedprojections carried by one of said members and engaging the other saidmember.

11. A method of forming an electric heater comprising the steps of p a.forming, from electrically resistive material, a heating element instrip form having two ends and a pair of opposed surfaces,

b. applying a coating of adhesive to one surface only of the saidelement to facilitate mounting of the said element on a surface to beheated,

c. applying discrete, electrically-conductive particles to the saidadhesive coating at the said ends of the I element,

d. bringing a pair of electrically-conductive terminal members intocontact with the said particles at respective said ends of the element,and

e. clamping each of the said terminal members to the said elementcausing the said particles to impinge onto the said element through thesaid adhesive coating providing an electrical connection between thesaid terminal members and the respective said ends of the element.

1. An electric heater comprising a heating element which is ofelectrically resistive material in strip form and which has two ends anda pair of opposed surfaces, a coating of adhesive on one surface only ofthe said element to facilitate mounting of the said element on a surfaceto be heated, a pair of terminals electrically connected to respectivesaid ends of the element, each terminal comprising anelectrically-conductive member, means clamping each said member to thesaid element, and discrete, electrically-conductive particles adheringto the said adhesive coating at the said ends of the element anddisposed under pressure between each of said members and the saidelement impinging onto the said element through the said adhesivecoating establishing electrical connection between the said members andthe respective said ends of the element.
 2. An electric heater accordingto claim 1, wherein the said adhesive is a thermo-set adhesive.
 3. Anelectric heater according to claim 1, wherein the surface of the saidelement remote from the said adhesive coating has bonded thereto a layerof electrically insulating material.
 4. An electric heater according toclaim 1, wherein the ends of the said element are of enlarged width. 5.An electric heater according to claim 1, wherein the said elementfollows a sinuous path.
 6. An electric heater according to claim 1,wherein the said element is supported by a readily removable backinglayer.
 7. An electric heater according to claim 1, wherein the saidadhesive coating extends over the whole of the said one surface of theelement.
 8. A method of establishing an electrical connection between anelectrically-conductive member and a thin electrically-conductiveelement which is to be supplied with electric current and which has apair of opposed surfaces, comprising the steps of a. applying a coatingof adhesive to one surface only of the said element, b. applyingdiscrete, electrically-conductive particles to a part of the saidadhesive coating, c. bringing the said member into contact with the saidparticles, and d. clamping the said member and the said element togethercausing the said particles to impinge onto the said element through thesaid adhesive coating providing the said electrical connection betweenthe said member and the said element.
 9. A device that includes anelectrical connection comprising a thin electrically-conductive elementhaving first and second opposed surfaces, an electrically-conductivemember disposed adjacent the first surface of the said element,discrete, electrically-conductive particles disposed between the saidelement and the said electrically-conductive member, a plate memberdisposed adjacent the second surface of the said element, a resilientpad disposed between the said element and the said plate member, andmeans clamping the said element between the said electrically-conductivemember and the said plate member to compress the said particles betweenthe said element and the said electrically-conductive member toestablish electrical connection therebetween.
 10. A device according toclaim 9, wherein the said clamping means includes a plurality ofdeformed projections carried by one of said members and engaging theother said member.
 11. A method of forming an electric heater comprisingthe steps of a. forming, from electrically resistive material, a heatingelement in strip form having two ends and a pair of opposed surfaces, b.applying a coating of adhesive to one surface only of the said elementto facilitate mounting of the said element on a surface to be heated, c.applying discrete, electrically-conductive particles to the saidadhesive coating at the said ends of the element, d. bringing a pair ofelectrically-conductive terminal members into contact with the saidparticles at respective said ends of the element, and e. clamping eachof the said terminal members to the said element causing the saidparticles to impinge onto the said element through the said adhesivecoating providing an electrical connection between the said terminalmembers and the respective said ends of the element.